Backport pull requests #18417 and #18478 (ActiveRecord: On reconnection failure, release only failed connetion)

[naag]

This is a backport of the pull requests #18417 and #18478 (ActiveRecord: On reconnection failure, release only failed connetion). It would be great to see this come back to 4.2 :-)

[guigs]

Thanks! I was debugging this error in one of my apps. Here is a monkey patch that works with Rails 4.0 and 4.1 (create a file in config/initializers):

ActiveRecord::ConnectionAdapters::ConnectionPool.class_eval do

  private

  def checkout_and_verify(c)
    c.run_callbacks :checkout do
      c.verify!
    end
    c
  rescue
    remove c
    c.disconnect!
    raise
  end

end